The organisation says they were part of a group of 600 females seized in raids by government troops and a regional militia group, the Popular Defence Forces.

Around $50 is paid per slave

In 1998, a series of raids terrorised the local population in Abyie in Southern Kordofan, a northern Sudanese province.

The area is on the front line in the long-running war between the Muslim-dominated government of the north and the rebel south, which is mainly Christian.

1,000 freed last month

Christian Solidarity says local traders are helping to arrange the freedom of the remaining slaves.

Last month, the organisation bought the freedom of more than 1,000 females enslaved by government-sponsored forces during raids near the government-held garrison town of Wau in neighbouring Bahr- el-Ghazal province.

A spokesperson for the charity said that around $50 per person is paid, mainly in the Sudanese currency.